What Is Cross-Over Cable?

In a Ethernet networking environment — like in a family home with multiple PCs that are wired — the computers must all connect to a central router. The router takes all the bits being sent out by the computers and relays them onto the other devices on the network, or out to the wider internet. However, a crossover cable can be used to connect two devices directly, without the need for a router in the middle.

It simply reverses some of the pins so that the output on one computer is being sent to the input of another. Some of us have fond memories of using a cross-over cable to play multiplayer games before the internet was a thing.

Connecting two machines is one use for a cross-over cable; the other is to expand a network by connecting another network switch, thereby giving you more ports. It’s always handy to have a length of cross-over cable around! Or is it?

Why You Probably Don’t Need A Cross-Over Cable

Having explained how a cross-over cable can be used, you ought to know that you probably don’t need one. Most network devices are now equipped with what’s called “autosensing”, or switchable “uplink” ports. These either use software to automatically detect when a port should be run in cross-over mode, or give you a physical switch that you can use to enable the mode. They do the pin cross-over in the switch hardware itself.

Even then, nearly all modern hardware will automatically detect what you’re trying to do and configure the Ethernet port appropriately, without the need for a cross-over cable.

What You’ll Need

Some Ethernet cabling, obviously. I’ll be using CAT5 today. Strictly speaking, CAT5e is certified for true gigabit support, but in practice plain old CAT5 cabling can be used just fine over short distances.

A crimping tool. This your all-in-one networking tool – specially shaped for pushing down the pins in the plug and able to strip the shielding off cables, as well as cut.

In addition to these tools, you’ll also need the diagram below, preferably printed out as a reference. Note that side A and B are not simply inverted:

Making The Cable

Start by threading some shields onto the cable, it will be easier to do it now rather than later.

Strip about 1.5cm of cable shielding from both ends. Your crimping tool should have a round area specifically for this task.

Untangle the wires (there should be 4 “twisted pairs”). Arrange them in the order shown on the sheet from top to bottom; one end should be in arrangement A, the other B.

When you’ve got the order correct, bunch them together in a line. If you have some that stick up beyond the others, snip them back to a uniform level.

The hardest part is placing these into the RJ45 plug without messing up the order. Hold the plug with the clip side facing away from you; the gold pins should be facing towards you, as shown below.

Push the cable right in — the notch at the end of the plug should just be over the cable shielding. If it isn’t, you stripped too much shielding off. Snip the cables back a little more.

When the wires are sitting tightly in the plug, insert it into the crimping tool and push down. In theory the crimper is shaped to the exact right size, but in practice I find pushing too hard can crack the brittle plastic plug.

Repeat for the other end, using diagram B instead.

If you don’t have a cable tester, the easiest way to test is just to plug it in. Try connecting two computers directly together. The status LEDs vary by device, but typically one will show activity while the other indicates speed.

Let us know in the comments what it is that you needed a cross-over cable for!

Most articles I have read only reverse the orange and green pairs, (recieve and transmit pairs).... the Blue and Brown pairs stay put. Why do you reverse them as well? Pins 4,5 and 7,8 are not used (except in PoE systems, and in those it would be important that green and brown pairs stay straight through) Im not a pro, but I think there is an error here.

That termination in your photo is still not very good. The jacket should be past the crimp bar, and the crimp bar comes down onto all of the untwisted pairs... That bar's purpose is to avoid tension on the cable from pulling on the wires that the pins crimp down onto.

I have done a lot of cable, normal and crossover and depending on the quality of cable the straightening of the cable is more or less difficult to obtain a good result. But its one of the most crutial part of making the cable.

James has a BSc in Artificial Intelligence, and is CompTIA A+ and Network+ certified. He's the lead developer of MakeUseOf, and spends his free time playing VR paintball and boardgames. He's been building PCs since he was a kid.